From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Mr. Royce's remarks on various 40/50 HP chassis piston designs.
| Identifier | ExFiles\Box 181\M11\ img144 | |
| Date | 25th February 1919 | |
| To BY.{R.W. Bailey - Chief Engineer} from E.{Mr Elliott - Chief Engineer} Copy to EH. " " EFC. RECEIVED [stamp with] 27 FEB 1919 ORIGINAL 25th February, 1919. E3/G25219. RE 40/50 H.P. CHASSIS PISTONS. [handwritten] X.3400 X.2748 Referring to your memo BY/RB{R. Bowen}5/F4219, I have been over these pistons with Mr. Royce, and the following is the substance of his remarks concerning them :- (1) [handwritten] X1499 E.6806 - Old type barrel piston in aluminium. Mr. Royce thinks this is not worth trying, as it possesses faults which we have cut out on later designs, such as piston rings too near the top edge. In any case, the strengthening frame bolted under the piston pin cannot be used, and the skirt should be considerably thicker to be practical in aluminium. (2) [handwritten] X2369 E.17403 - Zephyr "Eagle" type piston for car. Mr. Royce considers this design is not worth trying, as it is bound to knock badly. (3) (4) & (5) E.17022, 17372, and 17402 respectively. All these are to the die cast design, and are treated generally as follows:- We have very little faith in the design with the high piston pin. In all cases, however, more space should be left above the piston rings, or otherwise we shall not expect to keep the oil down. Two types should be made:- (a) [handwritten] X.3400B Low piston pin having .8" to .9" of piston above top ring. The part immediately above the top ring should run on the cylinder walls, and be eased off above that as required, not like E.17402. (b) [handwritten] X.3400C High piston pin having not less than .7" of piston above the top ring. Treat that portion of piston above top ring as specified in (a). Owing to the possibility of this No. 2 piston not keeping down the oil sufficiently, an extra scraper ring should be added under the piston pin with oil collecting groove and drain holes complete. This extra feature may spoil the design for die casting. If you are not satisfied with the method of securing the piston pin first proposed for die-cast pistons, try the tapered screw intended for E.6806. Pistons to compression ratios of 4.000 and 4.300 should be made. E.{Mr Elliott - Chief Engineer} | ||